PLAT-345 ensure sender object is passed to doEdit

It appears that the sender object has been missing from the parameter
list to Article::doEdit which is responsible for the work of creating
the welcome message. As a result, the $wgUser is being used as the
default author in a batch context which appears to resolve to localhost
or 127.0.0.1 in this context.
Adding IncludeMessagesTrait.

Adding the IncludeMessagesTrait and removed it from BaseTask. The new
trait seems to be a better location for this functionality.

/cc @nmonterroso
Integrate the IncludeMessagesTrait.
Merge pull request #4148 from Wikia/fix-hawelcome-submitted-by

PLAT-345 ensure sender object is passed to doEdit for correct welcome message attribution